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UPS Battery, is required to deliver high currents during short discharge times, to ride through
short power failures or until standby generator kicks in. To allow the high rate of discharge UPS
battery is designed with parallel connected thin plates in order to increase plate's active surface
area with the electrolyte.

Charging,  is accomplished by connecting battery terminals to a voltage source (charger) with
the proper polarity. While charging electrolysis of water decomposes, as a byproduct, water to
its ingredients. Oxygen gas is formed at the positive plate and Hydrogen gas at the negative plate.

During discharging the electrochemical energy stored in the electrodes is converted to electrical
energy. The electrochemical reactions during discharging, results in water and Lead Sulfate
which coats both electrodes, recharging restores the situation.

More information, including electrochemical reaction formulas, see  
Lead Acid Battery Basics
article.   


Flooded Lead Acid Battery.

In Flooded, also called Wet , or Conventional  Batteries, the oxygen and hydrogen gases formed
during charging are vented to the air. They  therefore require periodic maintenance, performed
by authorized personnel, in order to check the sate of the battery and refill the missing water, if
needed.
Due to hydrogen’s explosive nature the batteries should be located in separate unmanned and
well vented rooms. These  are generally used only in large installations, where long life and cost
/performance predominate, and where maintenance personnel is available.  


Maintenance Free Valve Regulated (VRLA), Sealed Lead Acid ( LSA) Batteries

In a Sealed  Battery, the possibility of gas venting to the air is eliminated. The oxygen diffuses
through the separator from the positive plate to the negative plate, where it is recombined with
the hydrogen to form water. These batteries do not require water
refilling and are therefore called also Maintenance Free batteries.

To enable the possibility of pressure relief, mainly during overcharging,   relief valves are
installed, to regulate to preset pressure level. Thus, UPS SLA batteries  are frequently  
called Valve Regulated Lead Acid (VRLA) type.

SLA batteries are considered dry type, generally spill proof and leak proof even in case of
container cracks or fractures. They can be located within the UPS as any other electrical
component.

Following features of the SLA  type cause manufactures’ to prefer VRLA technology for
Uninterruptible Power Supply  applications:  

  • Maintenance free, no water topping up is required during the whole service life.
       No equalization charge is normally required.

  • Non hazardous, have no restrictions for rail, road, sea or air transportation as part
        of the system or as separate items.

  • Rugged and vibration resistant. Can be shipped via parcel post or fast shipping service.

  • Non corrosive can be used for marine applications or wet environment.

  • Can be located in any position (horizontal or vertical), enabling design flexibility.

  • Allow location adjacent to each other or on top of each other (provided that weight and
    venting are considered). Compact packaging in the enables using internal batteries while
    increasing capacity and backup time.

  •  About 99% of the gas is recombined within the battery; practically no hydrogen is
    emitted to the air, can be located in manned locations, where normal venting exists.

  •  The UPS can be designed to allow replacement or hot swapping of failed batteries by the
    operators, or by local service people.

  •  High rate discharge ability. As requested for systems that provide high energies for
    relatively short times.

  • No memory effect. VRLA batteries retain their full charge in float condition during  
    lifetime.
What is a UPS Battery?
Operation and  Features of  Flooded and Maintenance Free VRLA
UPS Battery